1. Field
One or more embodiments described herein relate wafer fabrication.
2. Background
Semiconductor wafers are farmed using various techniques. One technique involves cutting a cylindrical ingot, grown using a Czochralski method, into thin disk shapes with a cutter and then chemically and mechanically grinding the surfaces thereof.
A process of forming a high purity crystalline layer with crystal orientations aligned on a surface of a single crystalline silicon wafer grown using the Czochralski method is referred to as an epitaxial growth method or, more simply, an epitaxial method. A layer formed using this method is called an epitaxial layer or an epi-layer, and a wafer including an epi-layer is called an epitaxial wafer. One type of epitaxial method is performed by a reactor which operates under high temperature conditions and which includes a susceptor on which a wafer is placed to grow an epi-layer.
Epitaxial methods have proven to have drawbacks. For example, n-type or p-type ions may migrate between a susceptor and an upper surface of a polished wafer. As a result, the edge of the wafer may be doped with ions to an undesirably high concentration. This is called auto-doping. Another drawback relates to the inability of a cleaning gas to completely remove a natural oxide layer from a wafer. As a result, reaction gas may be deposited on a rear surface of the wafer during epitaxial deposition, which is called haloing.
Auto-doping and haloing significantly degrade wafer quality and the corresponding semiconductor chip made from the wafer.
Another drawback relates to the heat generated from a heating source during chip fabrication. This heat places thermal stress on the wafer, which, in turn, may cause slip dislocation and increase surface roughness of a rear surface of the wafer, both of which may degrade the nano-quality of the wafer. In addition, a heavily and thermally stressed region may cause a defect to occur in a device process.
Another drawback of susceptors relates to wear during use. More specifically, because the wafer is placed on a susceptor during a heating process, the susceptor may be worn by friction. Even though a small portion of a silicon carbide coating layer formed on the susceptor may be damaged by the friction, the susceptor should be replaced with a new one. Otherwise, material such as graphite removed from the susceptor may cause an epitaxial reactor to malfunction. This increases operation costs of the epitaxial reactor.